Some seasonal water temperature patterns in the Hauraki gulf,New Zealand |
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| Authors: | L J Paul |
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| Institution: | Fisheries Research Division, Marine Department , Wellington |
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| Abstract: | The changing pattern of water temperature in the Hauraki Gulf at approximately two‐monthly intervals during one and one‐half seasonal cycles in 1965–66 was determined from sea surface temperatures and bathythermograph profiles. Surface and bottom temperatures ranged from 22.0°c and 20.5°c respectively in March to 12.5°c and 13.0°c in July‐September. Seasonal temperature ranges and short‐term variations were greatest in the shallow south‐west Gulf. In winter the Gulf water was coolest close to shore. It was typically isothermal in depth but a temperature inversion of approximately l°c frequently formed, probably because of the combination of strong winds and an increased outflow of cool, low salinity water from harbours and bays. A similar inversion in Colville Channel may have been caused by more complex tidal and/or ocean current conditions. In spring and summer the Gulf became thermally stratified, with warmest temperatures in the shallow areas. Thermoclines were generally irregular in position and size, and probably represented solar heating and minor current boundaries rather than a distinct separation of major water masses. In late summer and autumn bottom temperatures increased and almost equalled the maximum surface temperature. During autumn surface water temperatures close to land decreased rapidly to return the Gulf to its winter isothermal condition. Local factors (wind, rainfall, tides, depth of water, and proximity to land) probably influence sea temperatures in the Gulf. Seawards of a line from Cape Rodney to Cape Colville oceanic conditions prevail; water temperatures are more constant and increase to seaward in both winter and summer. Oceanic and Gulf waters meet and mix in the Rodney‐Colville area, and Gulf water is transported east through Colville Channel. The extent of oceanic water penetration into the Gulf at depth is unknown. |
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